1. Field of the Invention
The Mediterranean fruit fly, Ceratitis capitata (Wiedemann) is a worldwide agricultural pest affecting over 253 varieties of fruits and vegetables (Liquido et al. 1991. Misc. Publ. Entomol. Soc. Am. vol. 77, p. 1). The invention relates to a method for the synthesis of ceralure B1, a strong attractant for C. capitata which is used in traps to monitor and detect the insects.
2. Description of the Relevant Art
The Mediterranean fruit fly, commonly known as medfly, is found in tropical areas such as central America and Hawaii. Periodic accidental introductions of the pests into the continental United States have been controlled by an extensive trapping system which relies on an effective attractant for detecting and monitoring the insects. Due to these and other efforts such as Sterile Insect Technique (SIT), to date the U.S. remains free of established populations. The establishment of the pest in the U.S. would have serious agricultural ramifications, however, such as an increase in the use of pesticides and associated economic and environmental impacts and a decrease in fruit and vegetable exports, a multi-billion dollar industry (Jackson et al. Winter, 1985. Bulletin of the ESA. pp. 29-37).
Conventional trapping systems have utilized traps baited primarily with trimedlure, a synthetic male medfly attractant (Beroza et al., U.S. Pat. No. 3,016,329, 1962), and have generally been effective for detecting and monitoring medfly infestations for more than 30 years. Trimedlure is a mixture of 16 regio- and stereoisomers of tert-butyl esters of 4 (and 5)-chloro-2-methylcyclohexane-1-carboxylate, and over one million dispensers containing 2 grams of trimedlure are produced and sold annually for use as bait in detection traps.
More recently, ceralure, an iodo analog of trimedlure, has shown improved attraction capabilities (McGovern and Cunningham, U.S. Pat. No. 4,764,366, 1988). Comparative studies indicated that ceralure was both more attractive and more persistent than trimedlure in the field (Leonhardt et al. 1996. J. Entomol. Sci. vol. 31, no. 2, pp. 183-190). In addition, a study of 4 trans isomers showed that the ceralure B1 isomer was superior to the other three isomers investigated (Warthen et al. 1994. J. Chem. Ecol. vol. 20, no. 3, pp. 569-578).
Synthetic methods have been described for the production of ceralure B1 (Avery et al. 1994. Tetrahedron Letters. vol. 35, no. 50, pp. 9337-9338; Raw and Jang. 2000. Tetrahedron. vol. 56, pp. 3285-3290; Raw and Jang, U.S. Pat. No. 6,375,943, 2002), with yields of xcx9c30-33% from the commercially available trans-siglure acid.
I have discovered a method for the preparation of ceralure B1 which improves the yield up to about 58-65%, approximately double the yield of currently-known synthetic methods. In addition, the method may circumvent chromatographic separations and is amenable to industrial scale-up. In accordance with this discovery, it is an object of the invention to provide a novel method for the preparation of the synthetic medfly attractant ceralure B1.